The market place is replete with all manner of devices for playing games on a television receiver by generating video and synchronization signals which can be coupled to the antenna terminals of a home television receiver. Such game playing devices are well illustrated by U.S. Pat. Nos. 3,728,480; 3,778,058; 3,829,095; Re 28,507 and Re 28,598. The electronic game playing devices represented by these patents are game attachments for a raster scan display such as a home television receiver or television monitor and having electrical circuitry or components for generating signals which, when supplied to the raster scan display, will cause the display to show on the screen thereof moveable game playing indicia or symbols or spots.
When employing these game playing devices in conjunction with a home television receiver which normally is used for receiving broadcast programs, the output of the game playing devices is coupled to the antenna terminals of the television receiver. The game devices gain access to the television receiver via an r.f. oscillator and modulator. This unit generates an r.f. output typically on channel 3 or channel 4 which is modulated by the composite synchronization and video signal generated by the game playing circuits. A typical unit consists of an oscillator, a diode modulator and a bandpass filter. The output of the game device is conducted by a coaxial cable to the television receiver, where an impedance transformer is used to match the coaxial cable to the 300 ohm impedance of the television receiver.
Considerable difficulty has been experienced in suppression of the radiation from the r.f. oscillator and modulator to a level which will not cause interference to other television receivers operating on the same channel as the game. The radiation limit is established by FCC regulations.
One technique for reducing radiation is to locate the r.f. oscillator and modulator at the television receiver rather than at the game box and thus eliminate the transmission of r.f. energy over a length of cable from the game box to the television receiver. The problem with this solution is that the r.f. oscillator requires electrical power necessitating that in addition to the coaxial cable to carry video and synchronization signals from the game box to the modulator and oscillator, another conductor must be supplied to bring power to the oscillator. Alternatively, d.c. power can be applied via the coaxial cable outer conductor, however, resistors or chokes are then required to prevent shorting out of the video and synchronization signals.